Two tier multiple sliding window mechanism for multidestination media applications

ABSTRACT

Some media applications use media that contains multiple types of media components in it and media sources with access to this media must send each type of media component to one or more media rendering destination devices. Furthermore there may be multiple destinations that can receive a particular type of media component and the media must be received at each destination without losses. This invention describes a two tier packet buffer structure at the media source with primary and virtual packet buffers that ensures minimal memory use at the media source and minimal network use. Furthermore the use of a sliding window with each virtual packet buffer associated with each destination, independently keeps control and track of destination state, ensuring the correct receipt of media data at each destination.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Serial No. 61/512,924, filed Jul. 29,2011, entitled “Techniques for broadcasting media over a local networkto multiple destinations” the entire content of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is directed to network communications and todigital media sourcing, transmission and rendering.

SUMMARY OF THE INVENTION

The present invention is directed to media applications that use mediacontainers, media files or media streams that contain multiple types ofmedia components in it and that use a media source with access to thismedia to send each type of media component to one or more mediarendering destination devices. Each such media destination is tailoredto receive one of these media components. Furthermore there may bemultiple destinations that can receive a particular type of mediacomponent. For example, a media application might use a media file withone video media component and one stereo audio media component and wantto send this to two video rendering devices and four stereo audiodevices. In such applications, firstly it is important to avoidduplicating media data stored and manipulated in the media source inorder to avoid wasting media source memory. Secondly, it is important toavoid retransmitting the same media data over a network to avoid wastingnetwork bandwidth.

In addition the present invention is directed to media applications thatneed to send media to multiple destinations where the network link has ahigh likely hood of losing media data and it is necessary to recoverfrom such data loses and provide the destinations with correct data. Todo this it is necessary to maintain independent data receipt status atthe media source for each destination and to retransmit data that isneeded by each destination appropriately.

In addition the present invention is directed to media applications thatneed to control the overall media transfer rate to each of thesemultiple destinations independently.

This invention describes a two tier buffer structure at the mediasource, with primary media packet buffers and virtual media packetbuffers. There is one primary media packet buffer for each mediacomponent type. Each primary media packet buffer has a set of one ormore virtual media packet buffers associated with it. Each virtualpacket buffer is also associated with one of the media destinationdevices that take a media component type that is the same as the mediacomponent type in the primary media buffer. Media packets of aparticular media component type are only placed in one primary mediapacket buffer. Each virtual media packet buffer associated with thisprimary buffer gets a reference to this media packet and a referencecounter in the media packet is used to track how many entities are usingthis packet.

Furthermore, this invention describes a sliding window mechanism witheach virtual buffer that controls the transmission of media packets tothe associated media destination. The size of each sliding windowaffects the number of packets that may be in transit and thereforedetermines the packets that may be in transit independently to eachdestination device.

This design uses multiple buffers and references to media packets tominimize memory use at the media source and uses multiple slidingwindows on multiple virtual buffers to minimize network traffic whileguaranteeing the correct receipt of media data at each destination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an overview of the devices in a system in accordancewith one embodiment.

FIG. 2 illustrates a schematic of the devices in a system in accordancewith one embodiment.

FIG. 3 illustrates the use of separate TCP (Transmission ControlProtocol is one of the protocols of the Internet Protocol Suite)connections to multiple destinations.

FIG. 4 illustrates the use of RTP (Real-time Transport Protocoldeveloped by the Audio/Video Transport working group of the IETFstandards organization) to send data to multiple destinations.

FIG. 5 illustrates the overall two-tier architecture.

FIG. 6 illustrates details of the two tier buffers and relationships.

DETAILED DESCRIPTION OF THE INVENTION

Today there are many forms of digital media, many types of digital mediasources, many types of digital media playback (rendering) systems andlots of ways of connecting media sources to media playback systems.

Digital media, hereafter referred to as media, comes in many forms,formats and containers, including Digital Video Disks, media files andmedia streams. The media contents can be audio, video, images or metadata media components and various combinations of each. For example apopular audio format is known as MP3 and a popular video format is H264.MP3 is an audio-specific media format that was designed by the MovingPicture Experts Group (MPEG) as part of its MPEG-1 standard and laterextended in the MPEG-2 standard. H264 is a standard developed by theInternational Organization for Standardization (ISO)/InternationalElectrotechnical Commission (IEC) joint working group, the MovingPicture Experts Group (MPEG). Movies are typically multimedia formatswith a video and multiple audio channels in it. For example a 5.1 moviecontains 1 video channel (media component) and 6 audio channels (audiocomponents). 5.1 is the common name for six channel surround soundmultichannel audio systems.

Digital media sources include media devices such as Digital Video Diskplayers, Blu-ray players, computer and mobile devices, and internetbased “cloud” media services. Blu-ray Disc (BD) is an optical discstorage medium developed by the Blu-ray Disc Association. Internet basedmedia services include services such as Netflix™ and Spotify™. Netflixis a media service and trademark of Netflix Inc. Spotify is a mediaservice and trademark of Spotify Ltd. Digital media playback (mediarendering destinations) systems include computer based devices, laptopsand smartphones, as well as network audio and video devices. A SmartTVis an example of a digital media rendering device that can play mediafrom an internet (cloud) based media service such as Netflix™. ASmartTV, which is also sometimes referred to as “Connected TV” or“Hybrid TV”, is used to describe the integration of the internet and Webfeatures into modern television sets and set-top boxes, as well as thetechnological convergence between computers and these televisionsets/set-top boxes. An internet radio device is another example of adigital media rendering device.

The connectivity between these media sources and devices is varied, butis evolving over time towards network based connectivity using IPprotocols. This is because IP connectivity is convenient, ubiquitous andcheap. IP stands for Internet Protocol. An IP networked device is adevice that adheres to the Internet Protocol suite standard. TheInternet Protocol suite is defined by the Internet Engineering TaskForce [IETF] standards body. The Internet is a global system ofinterconnected computer networks that use the standard Internet Protocol(IP) suite.

IP networks come in many forms; the most prevalent being Ethernet basedwired IP networking. Ethernet is a family of computer networkingtechnologies for local area networks (LANs) that is standardized as IEEE(Institute of Electrical and Electronics Engineers) Standard 802.3. Inrecent years with the prevalence of mobile computing devices, Wi-Fi hasbecome the most popular means for connecting network devices wirelessly.Wi-Fi is a trademark of the Wi-Fi Alliance and a brand name for productsusing the IEEE 802.11 family of standards. A Wi-Fi network is a type ofIP network.

The convenience and benefits of IP networking means that all of thesemedia sources and playback systems, if not already network enabled, arebecoming network enabled. Many Blu-ray players now have Ethernet andWi-Fi network connectivity. Today most higher end TVs are smart TVs thathave network capability. Similarly audio play back devices and evenradios are network and internet enabled.

Mobile devices, such as mobile phones, tablets, readers, notebooks etc,are able to receive and store media and have powerful media (audio andvideo) capabilities and are connected to the internet via cell phonedata services or broadband links, such as Wi-Fi that are high bandwidthand can access online media services that have wide and deep content.

The use cases or applications of these various forms of digital media,media services and media sources and playback systems have beenevolving. Initially it was enough to connect a media source to a mediadestination over an IP network. This is widely used today with Internetbased media source services, such as Netflix and a computer as a mediadestination. Users watch Netflix movies streamed over a wired IP network(the internet) to a computer. This is a case of a single point (one IPsource) to single point (one IP destination) connection over a wired IPnetwork. Even though the Netflix media service may send the same mediato multiple households, each of these is a single point to single pointconnection TCP/IP connection. A further evolution of this is to use awireless, Wi-Fi connection, instead of a wired Ethernet connection. Thisis still a single point to single point connection.

The applications targeted in this invention are for a further extensionof the above use cases where the media source connects to multipledestinations rather than a single destination. These are single point(one IP source) to multi point (multiple IP destinations) applications.An example would be where a user is playing a 5.1 movie media file to awireless video playback device and 6 independent wireless audiodestinations making up a full 5.1 surround sound system. In this casethe media is going from one media source to 7 media destinationssimultaneously. In another example, a user is playing music from onemedia source to 6 audio playback systems placed around the home in 6different rooms.

In both of these cases, it is necessary to play (render) the media atall destinations time synchronously. Furthermore, it is necessary tolimit the use of resources at the media source, such as keeping memoryuse to a minimum. In addition, it is necessary with multiple devicesreceiving media to manage network bandwidth efficiently.

In some applications, the video media may be rendered through one path,for example a specialized hardware path, and the audio may be renderedthrough a different network path. When different media components of thesame media are going through different paths, it is necessary to keeppath delays (path latency) to a minimum. This is necessary to keep thedifferent media components time synchronized. In these applications,keeping media network transport latencies to a minimum is important.

Furthermore, when the network is Wi-Fi, network packet losses can behigh and it is necessary to mitigate these in order to deliveruninterrupted playback.

The general structure of these application are that of multiple IPnetworked media source devices choosing, connecting and playing media toone or more IP networked media playback devices over an IP communicationnetwork.

FIG. 1 shows an exemplary system 100 having multiple media sourcedevices 104 and multiple media destination devices 106.

FIG. 2 is a schematic diagram of such a media system 100 with one ormore IP network-enabled media source devices 104 and one or more IPnetwork enabled media destination devices 106 connected via an IPnetwork 120.

Referring to both FIG. 1 and FIG. 2, a media source device 104 can beany variety of computing devices that can originate digital mediaincluding computers (e.g. desktop, notebook 14, tablet 12, handheld),mobile devices (e.g. smart phone 10, electronic book reader, organizerdevices), as well as set-top boxes and game machines 16. The media isany form of digital media, including audio or video, images, data,and/or Meta data.

Media destination devices 106 are devices that can receive digital mediaover an IP network 120 and play this media. This includes IP-enabledaudio and/or video and/or imaging devices that can render audio or videoor images or combinations of these at the same time. Media destinationdevices 106 include computers (e.g. desktop, notebook 15, tablet 13,handheld), mobile devices (e.g. smartphones, tablets, notebooks 15),network enabled TVs 20, network enabled audio devices 18, 22. If themedia is audio, playing the media means rendering the audio such that auser can listen to the audio. If the media is video, playing meansrendering the video such that a user can view the media. If the mediaincludes both audio and video, it means rendering both the audio and thevideo. If the media is images, playing means displaying these images ona screen. In this description, media destination devices 106 may also bereferred to as media renderers or combinations of these terms.

In the media environment 100 of the present invention, each media source104 can send its media to a selected set of media destination devices106 for playback.

The network 120 and all networks used and described in this invention toconnect all devices, including the media sources 104 with the mediadestinations 106 may be any network that supports an IP protocol. Thisincludes any wired IP connectivity mechanism including Ethernet if wiredand if wireless it includes any wireless IP connectivity mechanismincluding Wi-Fi. If this 120 is a Wi-Fi network, then the network 120may include a Wi-Fi access point (AP) or Wi-Fi router 110 that managesthe network in infrastructure mode. Alternatively, the network 120 maybe using Wi-Fi Direct (Wi-Fi Direct is a standard of the Wi-FiAlliance), in which case the AP 110 may not be present. The IP network120 may also be connected to the internet 800 through a wide areanetwork connection 26. The source 104 may also have a remote device 114associated with it such as a remote control device connected via an IPor other communication link 116. In addition the source 104 or network120 may have additional optional devices 112 such as a NAS (NetworkAttached Storage) device that provides media.

IP networks can use several different types of messaging includingunicast, multicast and broadcast messaging. Messaging being the sendingof IP packets.

Unicast messaging is a type of Internet Protocol transmission in whichinformation is sent from only one sender to only one receiver. In otherwords, Unicast transmission is a one-to-one node transmission betweentwo nodes only. In unicasting each outgoing packet has a unicastdestination address, which means it is destined for a particulardestination that has that address. All other destinations that may hearthat packet ignore the packet, if the packet's destination address isnot the same as that destination's address. Broadcast is a type ofInternet Protocol transmission in which information is sent from justone computer, but is received by all the computers connected on thenetwork. This would mean that every time a computer or a node transmitsa ‘Broadcast’ packet, all the other computers can receive thatinformation packet. Multicast is a type of Internet Protocoltransmission or communication in which there may be more than one senderand the information sent is meant for a set of receivers that havejoined a multicast group, the set of receivers possibly being a subsetof all the receivers. In multicasting, each multicast packet isaddressed to a multicast address. This address is a group address. Anydestination can subscribe to the address and therefore can listen andreceive packets sent to the multicast address that it subscribed to. Thebenefit of multicasting is that a single multicast packet sent can bereceived by multiple destinations. This saves network traffic if thesame packet needs to be sent to multiple destinations. When the samedata needs to be sent to multiple IP destinations generally,Broadcasting or Multicasting, rather than Unicasting, provides the mostefficient use of the network.

In this description the terms Broadcast and Multicast may be used. Inboth Broadcasting and Multicasting, when messages are sent, they arereceived by multiple destinations. Therefore in the presentspecification, the terms Broadcast and Multicast may be usedinterchangeably to refer to one packet being received by multipledestinations. In some cases this description only says the media is sentor transmitted without specifying whether it is broadcast, multicast orunicast. In this case, it means any one of these methods may be used forsending or transmitting the media.

In this description, the terms Message and Packet are often used and maybe used interchangeably. A Packet is a data set to be sent or receivedon an Internet Protocol network. The Packet may or may not be the sameas an ‘Internet Protocol Packet’. A Message refers to the logicalinformation contained in such a packet. In this description, the termSegment may also be used to refer to a data set. A data set is a set ofbytes of data. Data may be any type of data, including media or controlor informational data. In this description the term data and packet mayalso be used interchangeable depending on context. Packet refers to adata set and data refers to data in general.

Many IP protocols are accessed from software programs via a Socketapplication programming interface. This Socket interface is defined aspart of the POSIX standard. POSIX is an acronym for “Portable OperatingSystem Interface”, which is a family of standards specified by the IEEEfor maintaining compatibility between operating systems.

Currently when the same media data needs to be sent to multiple networkdestinations, the general technique for doing so is to use datamulticasting to the multiple destinations that need to receive the data.

In such a system the media is multicast to all the destinations and itis up to each destination to attempt to render the media appropriately.If during rendering there is an error where a renderer does not receivenew media data or does not receive it correctly, the renderer may rendererroneous data and then attempt to recover and continue correct mediarendering from the point after the error when correct data is received.For example, during rendering of a H264 stream, if there is anincidental data drop out, the displayed image may pixilate briefly andthen recover.

In the applications envisioned here, there is a need to send media froma source to multiple media devices, such as TV and speakers in the samelistening and viewing space. Furthermore there is a need to send thismedia over a wireless network such as Wi-Fi.

For these applications, this means all of the media rendering devices,such as speakers, that are in the same listening or viewing zone, needto be precisely synchronized to each other, so the listener and/orviewer does not discern any unintended media experience.

Secondly, because the media is transported over wireless, there is avery high likely hood of a media error, where the media is not receivedat each destination reliably or uniformly. If using broadcast ormulticasts to send packets, the same broadcast or multi cast packet, maybe received at one destination but not received/heard by anotherdestination.

In order to synchronize the rendering of all media destinations, thisinvention uses a technique as described in U.S. patent application Ser.No. 11/627,957.

In this invention, in order to broadcast media over a Wi-Fi network, itis first necessary to recognize that broadcast or multicast media willnot be received at all destinations uniformly. Some destinations willreceive a multicast packet, while others will not.

IP networks were first designed to operate over wired networks. Bydesign, the packet communications on these networks were ‘best effort’.This means any packet transmitted on the network may not be received bythe intended destination. This is most often due to a collision, whereanother device starts to communicate at the same moment as the device ofinterest, thereby causing a collision. Another method of loss would bethe devices in the network path, such as routers, simply dropping thepacket, for example due to the lack of buffer space. Other reasons forloss could be that the wired line is simply noisy and the packettransmission got corrupted, though this is rare for the wired case vs.the wireless case.

In all these wired situations, it is generally the case, that if thetransmission, for example a multicast message, was received by onedevice on a ‘subnet’ or wire, all the other devices on the same ‘wire’or subnet also receive the transmission correctly. This is because inthe wired case, the noise or interference situation of a device on onepart of the wire is not so different from the noise situation at anotherpart of the wire. If the wired devices are connected via a switch ratherthan a hub, the same issues are true, the amount of noise orinterference is minimal.

However, when using Wi-Fi, the situation is more complex. In wireless,the noise, standing wave, reflection situation can change from inch toinch. Each device on the same subnet does not see the same RFenvironment as another device right next to it. This means that anytransmission, again for example a multicast message, will be receivedvery differently at each Wi-Fi device in the same network—even if theyare right next to each other.

Managed Receipt

This invention describes a mechanism for broadcasting data to multipledestinations and guaranteeing receipt at each destination.

One method of doing broadcasts with guaranteed receipt at eachdestination would be to use separate TCP connections to eachdestination. In this case, each TCP link would maintain a TCP packetbuffer at the source for each destination, copy packets that are to besent into each buffer, and then use a TCP type sliding window mechanismto send the packets to each destination. An example of this is shown inFIG. 3. Here, a source 104 is setup to send media packets to multipledestinations 106 numbered 1 through N, set ‘a’ 706 and 1 through M, set‘z’, 708. In this example, each set of destinations consist of multipledevices that take the same type of data. So in this example set ‘a’ 706may be N stereo audio devices that take stereo audio data, while set ‘z’may be N video devices that take video data and render it. The mediadata 700 is sent to each destination 106 using TCP, with a TCPconnection 704 to each device. As explained previously, with TCP, thismeans there is a TCP data buffer at the source 703 of each TCPconnection 704 and a data buffer at each TCP destination 705. The datapackets 710 put into the TCP data source buffer 703 are sent to eachrespective TCP destination 705 if the TCP source sliding window 711 willallow it. The sliding window 711 allows a certain number of packets tobe sent beyond the last one that was acknowledged as received by the TCPdestination 705. As packet receipts are acknowledged by the TCPdestination 705, the back of the sliding window 711 moves forward, whichwill then allow additional packets to be sent. While this system willwork, it is very wasteful of system resources. Firstly it is wasteful ofmemory at the source 104, as each packet 710 of a particular data type,selected by a demultiplexer, destined for devices of data type ‘a’ 706is duplicated in each TCP source buffer 703 for each TCP link 704.Secondly this system is very wasteful of network resources as eachpacket 710 is sent multiple times at least once for each TCP connection704 to each destination device 106. In the previous example, if therewere 4 stereo audio destinations 106 (type ‘a’ 706) and two videodestinations 106 (type ‘z’ 708), each audio packet would be transmittedat least 4 times on the network and each video packet would betransmitted at least 2 times on the network. This is of course verywasteful of network resources as it requires 4 times the stereo audiobandwidth and 2 times the video bandwidth of a single audio and singlevideo system. The source 104 memory use and network bandwidth useincreases proportionally to the number of destination devices 106.

FIG. 4 shows an alternative approach to doing this, used by protocolssuch as the Real-time Transport Protocol (RTP), which uses multicastingof packets rather than unicasting.

In such a system as shown in FIG. 4, outgoing packets 700 of aparticular type, separated out by a demultiplexer, are queued to be sentin an outgoing queue 740, 754. Packets are then multicast 744, 752 outonto the network 750. Each multicast packet is received by alldestinations 106 and the destination accepts the packet if it is part ofthe multicast address. In this case all packets sent from queue 740 onlink 744 which are destined for destination 106 set ‘a’ 706 areaddressed to multicast address ‘a’ and all packets sent from queue 754on link 752 which are destined for destination 106 set ‘z’ 708 areaddressed to multicast address ‘z’.

So, as in the previous example, if destination device set ‘a’ is stereoaudio devices and destination device set ‘z’ is video devices thenstereo audio packets 710 destined for device set ‘a’ 706 are onlypresent in one buffer 740 at the source and are only sent on the network750 once. Similarly video packets 712 are only buffered in one place andsent once. However, with this system there is no means to individuallymonitor the receipt status of packets and retransmit them if needed. Inthis system, if destination 106 number 1 receives packet number 5 748and another destination 106 numbered N in the same set ‘a’, 706 does notreceive packet number 5 in its buffer 746, then that packet is lost todestination number N.

This system saves media source 104 memory space and is not wasteful ofnetwork traffic, but it does not keep track of or aid in ensuring allpackets are received at their target destinations.

Therefore this invention uses a system with a two tier architecture andmultiple sliding windows as shown in FIG. 5.

This invention targets applications where media is being sent from amedia source 104 to many destination devices 106 where the destinationdevices can be grouped into subsets that take the same type of data. Forexample an application may consist of two video/TV devices that takeH264 video data and four stereo audio player devices that take 16 bitstereo audio data. In this case the optimum solution would be for themedia source 104 to send one set of video packets that are received byboth video devices and one set of 16 bit stereo audio data that isreceived by all 4 audio devices.

FIG. 5 shows the a general embodiment of this invention, where there area number of destination devices 106 that are grouped into sets ‘a’ 706through ‘z’ 708. Each set of devices takes a particular type of data.E.g. set ‘a’ 706 may be video devices that take H264 video data and set‘z’ may be stereo audio devices that take 16 bit stereo audio data.

This system contains primary buffers 722, 726 (common collections) wherepackets are put into for sending to the destinations 106. Each primarybuffer holds packets of a particular data type destined for a specificdevice set. A demultiplexer 701 selects (separates) which packets go inwhich primary buffer based on data type. Packets 700 to be sent to adestination are separated by data type and placed into the appropriateprimary buffer 722, 726.

Each packet 733, see FIG. 6 which shows more details of FIG. 5, has apacket identifier (PID) 731 that is unique for each packet and isincremented from the previous packet put into the collection 722, 726.Note FIG. 6 only shows detail for the primary buffer 722 in FIG. 5 andvirtual buffers 724; however the detail is the same for the primarybuffers 726 and virtual buffers 728 shown in FIG. 5. Also the discussionmay only refer to primary buffer 722 and virtual buffers 724; howeverthe discussion also applies in the same way to primary buffers 726 andvirtual buffers 728. Each packet also has a “references” number r, 732that is used to keep track of the number of references to it. Inaddition each packet also has a time stamp ‘t’ 736 that is used to keeptrack of its age. Each packet also of course contains media data 735 ofa particular type.

The system also contains a virtual queue 724, 728 for each of thedestinations 106 in the system. The virtual queue 724, 728 does notcontain packets; instead it contains a “virtual packet” that points 718to a packet in the common collection 722, 726. As shown in FIG. 6, thepacket 714 may not actually be located in the common collection 722, butinstead may reside somewhere else, with the common collection 722 onlyhaving a pointer 730 to where each packet actually resides in memory.

As each packet 714 is added into the common collection 722 for sending,a reference to it 715 is also added to each virtual queue 724 and thereferences number 732 in the packet 714 in the common collection is setto the same as the number of virtual queues 724 that have references tothe packet.

Periodically, each virtual packet queue 724 is processed for selectingpackets to be sent to the destinations. A packet is selected for sendingbased on a virtual queue 724 output PID 727; see FIG. 6, which points tothe next packet to send and the end of the sliding window 725. If theoutput PID 727 points to a packet that is beyond the end of the slidingwindow 725 end PID 723, then no more packets, from that virtual queue724, can be sent at the present. If the output PID 727 is not beyond theend of the sliding window 725 end PID 723, the virtual packet reference727 of the packet is then used to get to the packet in the commoncollection 722. This packet is then selected for sending and the outputPID 727 in the virtual output queue 724 is incremented once it isselected for sending. Note that even though the packet at the output PID727 is selected for sending, the reference to this packet remains in thevirtual output queue 724, as this packet may need to be resent.

All packets selected for sending are placed in the output queue 740 forsending to destinations. This is done by adding a reference 742 to thepacket in the common collection 722 in the output queue 740 andincrementing the packets reference counter 732. If the output queue 740already has a reference to a packet that has the same PID 731 as thepacket that is about to be placed in the output queue 740, the packet isnot placed in the output queue 740. This allows multiple virtual queues724 and their respective destinations 104 to need the same packet, butonly have the system send this packet out once to all destinations ifthey are being multicast from the output queue 740.

If the packets are being unicast to each destination, they are unicastto each destination associated with the virtual packet queue 724 thatthe packet was selected from.

The output queue 740 is processed periodically to multicast each packetin the queue onto the network. As each packet is multicast, thereference to it 742 is removed from the output queue 740 and the packetsreference count 732 is decremented.

Each destination 106 will periodically or a-periodically send anacknowledgement to the source 104. In the acknowledgement is informationon the highest consecutive PID received, the LastPID. The destination106 keeps track of the consecutive PIDs it received since the start ofcommunication. This is used by the source 104 to remove all virtualpackets 715 in the virtual queue 724, for that destination, that havePIDs 731 that are lower than or equal to this LastPID. When packets areremoved, if the window start PID 737 of the sliding window 725 point topackets that have been removed, the sliding window 725 window start PID737 is incremented until it points to a packet in the virtual queue 724that has not been removed. If this causes the window start PID 737 to beincremented a total of K counts, the window end PID 723 of the slidingwindow 725 is also incremented by K counts. This allows more packets tonow be sent before they will hit the new window end PID 723 of thesliding window 725.

The effect of this is that each sliding window 725 for a virtual buffer724 associated with a destination 106, is a count of the packets thatare in transit to that destination. The larger this sliding window sizeis the more packets that can be in transit to this destination. Thesmaller this size of this window, the fewer packets can be in transit.

In a Wi-Fi network each Wi-Fi transmission consists of an uplink messagefrom the transmission source to the AP and a downlink transmission fromthe AP to the final transmission destination. In this case the downlinkfrom the Access Point to each destination can have different RFconditions. The downlink to one destination may be operating at a lowbit rate due to distance while the downlink to a second destination maybe operating at a high bit rate. Therefore the transmission to eachdestination will need to have different rates. Using a sliding window725 per destination 106, allows the transmission rate to be set perdestination 106.

For each packet removed from a virtual queue 724, 726 or output queue740 if applicable, the references number 732 in the packet in the commoncollection 722 is decremented. If this reference number 732 is zeroafter decrementing, it means no packet queue, virtual packet queues 724or the output queue 740, reference this packet any more. This is becauseall destinations 106 that could receive this packet, have acknowledgedthis packet as being received. Therefore if the reference number 732 iszero, the packet is discarded from the common collection 722.

A separate garbage collection process may also be present that willperiodically check the common collection queue 722, 726. When packets714 are put in the common collection queue 722, 726, the packet timestamp ‘t’ 736, in the packet 733, is updated with the current time.During garbage collection, the age of each packet is computed bysubtracting the packets time stamp 736 from the current time. If thepackets age is older than a maximum age threshold the packet isdiscarded and all references to it in all virtual queues 724 and outputqueue 740 are removed.

During operation, each destination 106 will periodically send the source104 a list of missing PIDs. These are PIDs of packets it never received.The source will on receipt of this list of missing PIDs, retransmitpackets from the virtual packet queue 724 that have PIDs 731 that matchthe PIDs in the list of missing PID list to the destinations 106. Thiswill be done by going through the virtual queue 724 for that destinationand finding the missing PIDs 731 and adding these missing PIDs 731 tothe output queue 740. The packets in the output queue 740 are multicastto destinations as mentioned above. This means that if severaldestinations 106 and virtual queues 724 select a packet with the samePID to be resent, it is resent only once. The destination 106 may alsosend missing packet notifications a-periodically.

This two tier architecture with a primary queue for each data type andmultiple virtual queues for multiple destinations using the same datatype and where each virtual queue maintains destination state withindependent sliding windows and where a common output queue eliminatesduplicate transmission, ensures minimal memory use and minimal networktraffic while providing retransmission services to each destination toensure packet receipt.

The present invention has been described in particular detail withrespect to several possible embodiments. Those of skill in the art willappreciate that the invention may be practiced in other embodiments.First, the particular naming of the components, capitalization of terms,the attributes, data structures, or any other programming or structuralaspect is not mandatory or significant, and the mechanisms thatimplement the invention or its features may have different names,formats, or protocols. Further, the system may be implemented via acombination of hardware and software, as described, or entirely inhardware elements. Also, the particular division of functionalitybetween the various system components described herein is merelyexemplary, and not mandatory; functions performed by a single systemcomponent may instead be performed by multiple components, and functionsperformed by multiple components may instead be performed by a singlecomponent.

Some portions of above description present the features of the presentinvention in terms of methods and symbolic representations of operationson information. These descriptions and representations are the meansused by those skilled in the data processing arts to most effectivelyconvey the substance of their work to others skilled in the art. Theseoperations, while described functionally or logically, are understood tobe implemented by computer programs. Furthermore, it has also provenconvenient at times, to refer to these arrangements of operations asmodules or by functional names, without loss of generality.

Unless specifically stated otherwise as apparent from the abovediscussion, it is appreciated that throughout the description,discussions utilizing terms such as “determining” or the like, refer tothe action and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system memories orregisters or other such information storage, transmission or displaydevices.

Certain aspects of the present invention include process steps andinstructions described herein in the form of a method. It should benoted that the process steps and instructions of the present inventioncould be embodied in software, firmware or hardware, and when embodiedin software, could be downloaded to reside on and be operated fromdifferent platforms used by real time network operating systems.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored on acomputer readable medium that can be accessed by the computer. Such acomputer program may be stored in a tangible computer readable storagemedium, such as, but is not limited to, any type of disk includingfloppy disks, optical disks, CD-ROMs, magnetic-optical disks, read-onlymemories (ROMs), random access memories (RAMs), EPROMs, EEPROMs,magnetic or optical cards, application specific integrated circuits(ASICs), or any type of media suitable for storing electronicinstructions, and each coupled to a computer system bus. Furthermore,the computers referred to in the specification may include a singleprocessor or may be architectures employing multiple processor designsfor increased computing capability.

The methods and operations presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may also be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will be apparent to those of skill in theart, along with equivalent variations. In addition, the presentinvention is not described with reference to any particular programminglanguage. It is appreciated that a variety of programming languages maybe used to implement the teachings of the present invention as describedherein.

The present invention is well suited to a wide variety of computernetwork systems over numerous topologies. Within this field, theconfiguration and management of large networks comprise storage devicesand computers that are communicatively coupled to dissimilar computersand storage devices over a network, such as the Internet, publicnetworks, private networks, or other networks enabling communicationbetween computing systems.

The applications this invention are directed at that may be describedabove and any objects of this invention that are described above do notfully describe all the applications and objects of this invention andthese descriptions are not intended to be limiting in anyway or manner

Finally, it should be noted that the language used in the specificationhas been principally selected for readability and instructionalpurposes, and may not have been selected to delineate or circumscribethe inventive subject matter. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting, of the scopeof the invention, which is set forth in the following claims.

What is claimed is:
 1. A system for sending media over an IP network tomedia rendering devices, comprising: an internet protocol communicationnetwork; a first plurality of one or more first media rendering devicesthat take a first media data type and adapted to communicate with thecommunication network; a second plurality of zero or more second mediarendering devices that take a second media data type that is differentfrom the first media data type adapted to communicate with thecommunication network; and a media source adapted to communicate withthe communication network and having access to media containing mediadata of the first media data type and of the second media data type,wherein the media data is grouped into packets of data wherein eachpacket comprises a set of media data, a reference counter field and aunique sequentially incrementing packet sequence number stored in apacket sequence number field; wherein the media source further comprisesa primary packet buffer for holding data packets of the first media datatype and a plurality of virtual packet buffers each comprising aplurality of packet sequence number references corresponding to aplurality of data packets of the first media data type that arecontained in the primary packet buffer, each virtual packet buffer beingassociated with only one of the first plurality of media renderingdevices; wherein a first packet of the first media data type is put inthe primary packet buffer and a packet sequence number reference to thefirst packet is placed in each of the first virtual packet buffers, andthe references counter field of the packet is set to the number of thefirst virtual packet buffers that have a packet sequence numberreference to the first packet; and wherein the first packet in the firstvirtual packet buffer is sent to the first media rendering device. 2.The system of claim 1 in which the media source receives from a firstmedia rendering device a received number that is the highest consecutivepacket sequence number in the packets it has received and; wherein themedia source removes references to all packets with a packet sequencenumber that is lower than or equal to the received number from thevirtual packet buffer associated with the media rendering device anddecrementing the references counter field in each packet removed fromthe virtual packet buffer.
 3. The system of claim 1 in which a firstvirtual packet buffer in the media source maintains a first packetindex, referencing the first packet stored in the first virtual packetbuffer, and maintains a next packet index referencing the next storedpacket in the first virtual packet buffer that may be sent to the mediarendering device associated with the first virtual packet buffer; andwherein the packet referenced by the next packet index is sent to themedia rendering device associated with the first virtual packet bufferand the next packet index of the first virtual packet buffer isincremented after sending the packet.
 4. The system of claim 3 whereinthe first virtual packet buffer will not send the packet referenced bythe next packet index if the size of the difference between the nextpacket index and the first packet index is larger than a windowthreshold.
 5. The system of claim 1 wherein the primary packet bufferholds a reference to the packet data.